Another source of material would be the samples from the Inform 7 manuals, but these aren't complete games and I am unsure what the usage rights are. Might be better for a mini-comp or something, where you take a sample and then expand upon it. http://inform7.com/learn/manuals/

*edit*Found the usage rights for the examples in the manual and it looks like they would be fair game for a comp or something.